Bombetoka Bay, Madagascar
Bombetoka Bay, Madagascar, satellite image. This bay links the Betsiboka River (at right) with the Mozambique Channel (top left), part of the Indian Ocean. The river carries a large amount of sediment, which has led to the development of several silt islands. The edges of these are green as they have been colonised by mangroves. The heavy sediment load is largely due to deforestation along the river's banks to make way for agriculture. Crops including rice and coffee are extensively grown in the area. This image, which is around 30 kilometres square, was taken by the ASTER instrument on the Terra satellite.
© NASA/SCIENCE PHOTO LIBRARY
Iridescent ammonite fossil
Iridescent ammonite fossil. This fossilised ammonite displays pearl-like colours of iridescence, which only become visible when the outer shell has been peeled away. Iridescence is an optical phenomenon caused by interference within light rays reflected from a translucent multilayered surface. In this case, the surface is the finely layered aragonite in the ammonite shell. This ammonite (20 centimetres across) is Cleoniceras cleon, from Cretaceous sediments in Madagascar. Ammonites displaying iridescence like this are often sold as gemstones, and have been officially recognised as such under the name ammolite.
© DIRK WIERSMA/SCIENCE PHOTO LIBRARY
Africa, topographic map
Africa, topographic map. Highlands and lowlands of the continents are shown as ridges and flat areas. Southern Europe and the Middle East are also seen at top and upper right respectively. The seabed depth varies from shallow (light blue) on the continental shelves, to deep ocean basins (dark blue). Topographic and bathymetric data is usually gathered by using aerial and satellite imagery combined with radar and sonar mapping. The satellites in this case were NOAA's POES satellites.
© PLANETARY VISIONS LTD/SCIENCE PHOTO LIBRARY